Method of manufacturing structural units

ABSTRACT

A method of producing an improved structural unit with anisotropic load characteristics includes producing a multiplicity of first building elements that are constructed from fiber-reinforced plastics material; producing at least on second building element that is of a different material to the first building elements; and adhering the first and second building elements together to form the improved structural unit.

FIELD OF THE INVENTION

THIS INVENTION relates to a method of manufacture of structural units.In particular, the invention relates to structural units constructed atleast partially from fibre-reinforced plastics.

BACKGROUND OF THE INVENTION

The superior physical properties of fibre-reinforced plastic are wellrecognised. However, to date, there have been difficulties withproducing viable structural elements of fibre-reinforced plastic due tocost constraints.

One approach used to produce fibre-reinforced plastic structuralelements has been to use large moulds to produce the structural element.However, the mould that is required is specific to that application.Therefore, if another structural element needs to be produced, anothermould is required reducing cost effectiveness. Further, this type ofmanufacture of fibre-reinforced plastics to produce structural elementsis difficult due to shrinkage and high temperatures, making the mouldsdifficult to produce.

Another approach to producing fibre-reinforced plastic structuralelements has been through the use of pultrusion. This method sufferssignificantly less from the problems of shrinkage or temperaturecontrol. However, the dies and machines needed are expensive to produce.Further, the dies are specific to a single application and pultrusioncan only be used for structures of continuous cross-section. That is,many complex shapes cannot be produced using pultrusion.

One problem associated with both methods is that any structure that isproduced is limited to the inherent physical characteristics of the typeof fibre-reinforced plastics. In many instances, this limits the use offibre-reinforced plastic for a particular application.

For a representative example of the prior art approach to compositestructures, reference may be made to U.S. Pat. No. 5,794,402, in thename of Dumlao et al. This patent describes a modular structural sectionincluding a beam and a load bearing deck formed of a polymer matrixcomposite material. The deck is described as a sandwich panel having alower surface, an upper surface and a core of hollow, elongate coremembers.

The Dumlao method bonds together fibre composite modules made ofspecific resin and fibres to make a larger structure, The largerstructure is made only from the materials of the individual modules and,therefore, has essentially the properties of the specific resin andfibres. The larger structure does not have any particular structuraladvantages compared to the modules.

OBJECT OF THE INVENTION

It is an object of the invention to overcome or alleviate one or more ofthe above disadvantages or provide the consumer with a useful orcommercial choice.

It is a further object of the invention to enable structural units to beproduced that have improved load carrying characteristics,

It is a still further object of the invention to allow structural unitsthat use fibre-reinforced plastic to be produced cost effectively.

SUMMARY OF THE INVENTION

In one form, though not the only or broadest form, the invention residesin a method of producing an improved structural unit with anisotropicload characteristics, said method including the steps of:

-   -   producing a multiplicity of first building elements that are        constructed from fibre-reinforced plastics material;    -   producing at least one second building element that is of a        different material to said first building elements; and    -   adhering said first and second elements together to form the        improved structural unit.

The inventor has found that a surprising advantage is obtained bybringing together disparate materials with quite differentcharacteristics to form structural units that can be built intostructures. The properties of the structures, such as stiffness,strength and mass, are tailorable by selection of the materials of thefirst and second building elements. The properties are tailorable asboth the first and second building members are able to withstand loadingin their own right. That is, the individual building element would beable to be loaded if they were not adhered together.

The first building elements may be produced using polyester, vinylesteror epoxy resin plastics and produced using a glass, carbon or keviarfibre. Preferably, the first building elements are pultruded.

The second building elements may also be produced using fibre-reinforcedplastic but with a different plastic and/or fibre to that of the firstbuilding elements. The second building element may also be produced fromany suitable material such as concrete, timber, plastics, metal or thelike, The concrete may be prefabricated or cast in situ.

The second building element may be used to improve the load carryingcharacteristics of the structural unit. The second building element mayprovide additional tensile, sheer or compressive strength to thestructural member.

Preferably, the first and/or second building elements have at least twosides of its outer periphery that are substantially flat.

The second building element may be placed between two first buildingelements. Alternately, the second building element may be locatedadjacent said first building elements.

The first building elements may be of uniform cross-section throughouttheir length. The first building elements may be tubular. The firstbuilding elements are produced using standard shapes and/or lengths.

The first and second building elements may be of a variety of differentshapes and/or different sizes.

Preferably, the building elements are adhered together using adhesive.The adhesive may be used not only to bond building elements together,but to absorb stresses and/or potential cracking that may occur when twodifferent materials are combined together. The adhesive may be epoxyresin.

The building elements may be adhered to each other to enable thestructural unit to be curved.

Bulkheads, diaphragms, strong points and/or internal ties can be used toproduce the structural units.

The structural units produced using this method may be used inconjunction with each other to produce an improved structure.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention, by way of example only, will be describedwith reference to the accompanying drawings in which:

FIG. 1A is a perspective view of a beam according to a first embodimentof the invention;

FIG. 1B is transverse cross-sectional view of the beam according to FIG.1A;

FIG. 2A is a transverse cross-sectional view of a floor slab unitaccording to a second embodiment of the invention;

FIG. 2B is a transverse cross-sectional view of a floor slab unitaccording to a third embodiment of the invention.

FIG. 3A is a transverse cross-sectional view of a girder according to afourth embodiment of the invention.

FIG. 3B is a transverse cross-sectional view of a girder according to afifth embodiment of the invention;

FIG. 4 is a transverse cross-sectional view of a curb unit for bridgesaccording to a sixth embodiment of the invention;

FIG. 5A is a perspective view of a pole according to a seventhembodiment of the invention;

FIG. 5B is a transverse cross-sectional view of a pole for bridgesaccording to a sixth embodiment of the invention;

FIG. 6A is a side view of a pedestrian bridge according to an eighthembodiment of the invention;

FIG. 6B is a transverse cross-sectional view of the pedestrian bridge ofFIG. 6A;

FIG. 6C is perspective view of a rail of the pedestrian bridge of FIG.6A; and FIG. 7 is a side view of a pedestrian bridge according to aninth embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1 B show a beam 10 produced using two different standardtypes of pultruded fibre-reinforced plastic members 11 and 12 and aconcrete member 13.

One type of fibre-reinforced plastic member 11 is tubular andsubstantially square in transverse cross-section. These fibre-reinforcedplastic members 11 are constructed from polyester plastics and glassfibre making them relatively cheap to manufacture.

The other type of fibre-reinforced plastics member 12 is substantiallyplanar and constructed from vinylester plastics and carbon fibre and issubstantially stronger than the other fibre-reinforced members 11.

The concrete member 13 is prefabricated prior to the beam being formed.

The beam 10 is produced by gluing the fibre-reinforced members 11 and 12and concrete member 13 together using epoxy resin. The combination ofthe two different fibre-reinforced plastic members 11 and 12 providesthe beam 10 with excellent tensile strength whilst the concrete member13 provides the beam 10 with excellent compressive strength. This allowsa lightweight, structural beam 10 to be produced quickly and easily withreduced cost.

The beam 10 has considerable advantages compared to the known prior artcomposite modules. Careful selection of the fibres and resins for thefibre-reinforced members 11 and 12 allows the properties of the beam tobe tailored to provide the desired strength, stiffness, mass, etc. Itwill be appreciated that selection of the glue for bonding thefibre-reinforced members and the concrete member 13 is important toallow for variations between thermal expansion properties of differentmaterials. The glue also absorbs stresses that can lead to crackingwhich is known to be a problem in prior art composites.

FIG. 2A shows a floor slab 20 comprising two different standard types ofpultruded fibre-reinforced plastic members 21 and 22 and a prefabricatedconcrete slab 23.

The fibre-reinforced members 21 are tubular and substantially square intransverse cross-section. These fibre-reinforced plastic members 21 areconstructed from vinylester plastics and glass fibre giving them goodtensile strength properties.

The fibre-reinforced plastics members 22 are substantially planar andconstructed from epoxy resin plastics and carbon fibre and aresubstantially stronger than the other fibre-reinforced members 21.

The fibre-reinforced members 21 and 22 and concrete member 23 areadhered together using epoxy resin. The fibre-reinforced members 22 arelocated between the fibre-reinforced members 21 and are located at thebase of the floor slab 20 to increase the tensile strength properties ofthe floor slab 20. The concrete slab 23 provides compressive strength tothe floor slab. Hence, a modular lightweight floor slab 20 can beproduced quickly and easily.

A variation of the floor slab 20 of FIG. 2A is shown in the floor slab30 of FIG. 2B. Again, two different standard types of fibre-reinforcedplastics member 31 and 32 and a cast in situ concrete slab 33 are usedto produce the floor slab 30.

In this embodiment, the fibre-reinforced members 31 and 32 are arrangedin a different fashion according to differing load requirements of thefloor slab.

The fibre-reinforced member 32 is elongated and extends along the baseof the floor slab 30. In this embodiment, it is more practicable tolocate the fibre-reinforced member 32 along the base of the floor slabas it reduces labour time in constructing the slab without substantiallydecreasing the structural properties of the floor slab 30.

FIG. 3A shows a girder 40 comprising fibre-reinforced plastic members 41and a steel sheet 42.

The fibre-reinforced plastic members 41 are tubular and substantiallysquare in transverse cross-section. These fibre-reinforced plasticmembers 41 are constructed from polyester plastics and glass fibre.

The steel sheet 42 is constructed of an impact resistant steel and hasanti-slip indentations (not shown) located on its upper surface.

The girder is produced by adhering the fibre-reinforced members andsteel sheet together using epoxy resin. The fibre-reinforced membersprovide tensile strength whilst the steel provides compressive strengthand wear resistant surface.

The girder is typically used as the body for a trailer of an articulatedvehicle. The girder is lightweight and has good strength and wearcharacteristics.

FIG. 3B shows a girder 50 that is a variation of the girder 40 of FIG.3A. The girder 50 uses different shaped fibre-reinforced plastic membersto produce a different shaped lower section of the girder. This isuseful for a different wheel configuration for a trailer of anarticulated vehicle.

FIG. 4 shows a curb unit 60 for a concrete bridge 61. The curb unit isproduced using fibre-reinforced plastic members 62, a concrete block 63and post 64.

The fibre-reinforced members 62 are constructed from polyester plasticsand glass fibre and are shaped as described previously.

The fibre-reinforced members 62 are adhered to each other and to theconcrete block 63. The post 64 is attached to the concrete block 63using conventional fastenings 65.

The curb unit 60 is then attached to a side of a bridge 61 usingadhesive. The curb unit is lightweight and strong and can resist forceapplied to the pole 64 in any direction due to the construction of thecurb unit 60.

FIGS. 5A and 5B show a pole 70 comprising two laminate wood halves 71and twenty-four fibre-reinforced plastic members 72.

The fibre-reinforced members 72 are made from polyester plastics andglass fibre. They are tubular and have a curved top and bottom surface.

The pole 70 is produced by adhering the fibre-reinforced plastic members72 together and then adhering the laminate wood halves 71 to thefibre-reinforced members 72.

The pole 70 that is produced looks similar to an actual timber pole butis lightweight, strong and is can be made more fire resistant.

FIG. 6A and FIG. 6B show a pedestrian bridge 80 comprising a pair ofrails 81 and 82 constructed from fibre-reinforced plastics members 83.

The fibre-reinforced members 83 are made from vinyl ester plastics andglass fibre. They are tubular and rectangular in cross-section.

The rails 81 and 82 are constructed by banding the fibre-reinforcedplastics members 83 prior to adhering them to each other. This pressstresses the fibre-reinforced members as well as creating a desiredshape. Shorter fibre-reinforced members 83A can be used to createwindows 84 within the rails.

FIG. 6C shows the rail where plastic fibre members 83B have been adheredtransverse to the other plastic fibre members 83. These transversemembers can be applied along the length of the member 83 to provideadditional stiffening to the rail to prevent distortion and buckling andassist in carrying shear forces.

FIG. 7 shows a further embodiment of a pedestrian bridge 90 constructedfrom fibre-reinforced plastic members 91. The lower fibre-reinforcedplastics members 91A do not extend the length of the bridge to provideadditional clearance under the bridge 90.

An advantage of this method of producing the variety of structuralunits, in those described above, is that structural units can be madeaccording to specific engineering requirements. Different materials canbe combined with fibre-reinforced plastic to produce the desiredanisotropic load characteristics of the structural units.

Further, this method can be used to produce structural units that usefibre-reinforced plastic relatively cheaply and easily, whereaspreviously it has been impractical to do so due to cost. This methodemploys relatively small transverse cross-sectional shaped lengths ofpultruded material that can be manufactured cost effectively due toeconomies of scale, This cost saving can be achieved as standard shapesare used for a variety of applications without the need to manufacturenew dies,

It should be appreciated that various other changes and modificationsmay be made to the embodiments described without departing from thespirit or scope of the invention.

1. A method of producing an improved structural unit with anisotropicload characteristics, said method comprising: producing a multiplicityof first building elements that are constructed from pultrudedfiber-reinforced plastics material; producing at least one secondbuilding element that is of a different material to said first buildingelements; and adhering said first and second building elements togetherto form a structural unit having anisotropic load characteristics. 2.The method of claim 1 wherein the first building elements are producedusing polyester, vinylester or epoxy resin plastics and produced using aglass, carbon or kevlar fiber.
 3. The method of claim 1 wherein thesecond building elements are produced using fiber-reinforced plastic butwith a different plastic and/or fiber to that of the first buildingelements.
 4. The method of claim 1 wherein the second building elementis produced from concrete, timber, plastics, metal or the like.
 5. Themethod of claim 4 wherein the concrete maybe prefabricated or cast insitu.
 6. The method of claim 1 wherein the second building element isused to improve the load carrying characteristics of the structuralunit.
 7. The method of claim 1 wherein the second building elementprovides additional tensile, sheer or compressive strength to thestructural member.
 8. The method of claim 1 wherein the first and/orsecond building elements have at least two sides of its outer peripherythat are substantially flat.
 9. The method of claim 1 wherein the secondbuilding element is placed between two first building elements.
 10. Themethod of claim 1 wherein the second building element is locatedadjacent said first building elements.
 11. The method of claim 1 whereinthe first building elements are tubular.
 12. The method of claim 1wherein the first building elements are produced using standard shapesand/or lengths.
 13. The method of claim 1 wherein the first buildingelement is shaped differently to the second building element.
 14. Themethod of claim 1 wherein the building elements are adhered togetherusing adhesive.
 15. The method of claim 14 wherein the adhesive absorbsstresses and/or potential cracking between the two building elements.16. The method of claim 15 wherein the adhesive is an epoxy based. 17.The method of claim 1 wherein the building elements are adhered to eachother so that the structural unit is curved.
 18. The method of claim 1wherein bulkheads, diaphragms, strong points and/or internal ties areused to produce the structural units.
 19. A structural unit produced inaccordance with claim
 1. 20. A structural unit comprising: amultiplicity of first building elements that are constructed frompultruded fiber-reinforced plastics material; at least one secondbuilding element that is of a different material to said first buildingelements; and the first and second building elements being adheredtogether to form a structural unit having anisotropic loadcharacteristics.